Electron discharge apparatus



Feb. 22, 1944. 1 H. FREMUN 2,342,263

A ELECTRON DISCHARGE APPARATUS Filed NOV. 27, 1940 Ldlllnmummw B/ 1 l ll l BLMZLQMW Patented Feb. 22, 1944 ELECTRON DISCHARGE APPARATUS JohnHeaver Fremlin, London, England, assignor to International StandardElectric Corporation, New York, N. Y.

Application November 27, 1940, Serial No. 367,400 In Great BritainDecember 22, 1939 (Cl. Z50-36) 6 Claims.

This invention relates to high frequency electron discharge apparatus ofthe kind wherein electrons are caused to oscillate about a positiveelectrode.

The apparatus of the invention comprises means for directing an electronbeam over a finite path the potential distribution along which issubstantially parabolic so that the field acting upon the electrons atany point in said path is directly proportional to the spacing of thatpoint from a fixed intermediate point in the path about which fixedpoint the electrons are to oscillate.

Further features of the invention and the advantages derived by the useof the invention will become clear in the following description ofcertain embodiments given with reference to the accompanying drawing, inwhich Figs. 1, 1a, 1b, 2, 3 and 4 are greatly enlarged cross-sectionalViews of Vacuum tube elements in accordance with the invention.

The structure of Fig. 1 comprises a cathode C with a control grid G,anode A and anti-cathode L. The figure is a cross-section of the actualstructure which consists of a series of parallel rods extended in adirection perpendicular tothe paper.

Now it will be seen that if the electrodes G and L are normally atcathode potential and the anode rods have a considerable positivepotential, electrons from the cathode which pass between the rods G willtend to move across the gap towards the anti-cathode L. In a preferredembodiment means are 'provided for setting up a magnetic eld along aline cl running from a point c on the surface of cathode C to a point onthe surface of anti-cathode L and through the centers of these elements.This magnetic eld is used to ensure that the electrons do not leave thestraight path cl. The shape and position of the various electrodes inthe tube are so arranged that the potential distribution along the linegl is as far as possible `parabolic in form g being the point on line cldetermined by the intersection with line cl of a line passing throughthe centers of grid elements G. This being the case, the eld acting uponan electron at any point will be directly proportional to its distancefrom the point O, this point being approximately midway between g and l.It is assumed throughout that the potentials of G and L are nearlycathode potential. The indicated potentials of A, C, G and L may bemaintained' by appropriate connections to a source of potential such asbattery B.

Now, it is clear that in this circumstance an electron in the space g tol will experience a force which is proportional to its distance from Oand is always directed towards O, i. e., the electron will be naturallyurged in generally simple harmonic motion about O, and this motion willbe accurately synchronous, even though it may gain or lose energy duringthe period lof oscillation about O.

The fornr of potential distribution described necessitates the use of amagnetic concentrating field for the working of the valve. (Polepieces Mindicate diagrammatically a. means for producing a magnetic field.) Thisappears from the fact that if the potential distribution along gl isparabolic with a potential maximum at `O, from Laplaces equation itfollows that a little way off the line gl there` must be a eld away fromthe line gl which would tend, if any electron deviates from the centreline, to drive it further away still from that line. No possiblearrangement of electrodes could in itself prevent this phenomenon if aparabolic potential distribution is to be taken on the centre line.

In Fig. l the parabolic field distribution along the line gl is attainedby making the anode rods of large diameter perferably greater than theirspacing and comparable with the dimensions Ol, Og, the grid andanti-cathode rods being of relatively small diameter. If the anode roddiameter is reduced and the distance between centres remains unchangedthe anode potential .has to be increased. The precise relation betweendimensions and potentials can be found by means of a rubber sheet model,probes corresponding to the electrodes being adjusted against oppositesides of the sheet until the sheet conforms to a parabolic templateplaced along the axis of symmetry of the probes.

The new requirements are compared with the usual conditions inBarkhausen Kurz oscillators in Figs. 1a and 1b. In Fig. la theequipotential lines (dotted) and the corresponding parabolic voltagecurve (chain line) are shown for the structure of Fig. 1, while Fig. 1b'shows the potentials in the case of a, planecathode CZ,` positive meshgrid GZ and plane anti-cathode L2.`

The'mode of action of the tube lof Fig. 1 is as follows: l Y

Imagine a continuous emission of electrons from the cathode C betweenthe two' wires of the grid" G. These electrons will normally travelacross to L where some of them will be collected and the rest will bereflected back towards the cathode. Now suppose that the electrode L isfore will be removed permanently from the nurnber of electronsoscillating in the space gl. the other hand, electrons which pass O asthe electrode L begins to go negative with respect to its normalpotential will lose energy to the oscillation, and in consequence alarger number of them than usual will be reflected andv fewer will becollected by the electrode L.

Of the continuous motion of electrons from the cathode C more of theseelectrons which are moving in such a phase as to give energy to the On noscillation are preserved than there are of elec- Y trons moving in sucha phase as to absorb energy from the oscillation. In consequence ofthis, the oscillation on balance gains energy from the electron beam,and will build itself up further.

The output may be taken from the anticathode rod L and one of the otherelectrodes for example by extending the rods to form a tuned Lecher wiresystem.

The structure may be made symmetrical as shown in Fig. 4 by providingadditional rods G1, A1, L1 similar to those shown in Fig. 1 on theopposite side of the cathode and similarly connected to potential sourceB. There are, then, two oscillating electrodes, L and a second L1symmetrically disposed with respect to the capacities of the rest of thevalve, and these two electrodes may be used as output electrodes. Theymay be sealed straight from the top of the closed bulb in which thevalve is built and tuned directly as a pair of Lecher wires to anydesired frequency.

In such case it is found that when this external Lecher wire system istuned to suitable` wavelengths, the valve itself begins to oscillate.The frequency of oscillation is found to coincide very well with thecalculated frequency of oscillation of the electrons in the space gl,thus showing that the valve is operating in the expected manner. Thefrequency of oscillation depends rst upon the linear dimensions of thevalve, and

secondly upon the potential of the accelerating electrodes-A. It ispossible, then, with a good valve, by varying the potential of A, toobtain oscillations of a wide range of wavelengths. This gives the valvea marked advantage over the valves of the Barkhausen type, in which thefrequency range is very much limited. It is quite possible to obtainoscillations with potentials between 100 volts and 1000 volts on theelectrodes A, which gives us a variation of frequency by a.

factor greater than 3. It is also possible in some special circumstancesto obtain waves of this type in which apparently the oscillation of theLecher wire system has a frequency double that of the electrons in thespace gl. This would extend the frequency range ofthe valve stillfurther.

It is not proposed that thisv valve should be used for the production ofhigh powers. Its construction, with thin metal rods, and its necessarilysmall size preclude the possibility that very high powers can bedistributed safely. Its Wide frequency range. hQWeVerimakesit Suitable.

that it is very dicult mechanically to construct ale/12,263

for use for example as a receiving valve. In one suitable receivingarrangement, it is proposed to work super-regeneratively, using aquenching oscillation at about 5 megacycles, which can best be put onthe grid of the valve. It has been found that if the grid potential ischanged considerably from the optimum for oscillations, the oscillationsare suppressed. If, then, superimposed upon the direct grid potential,we have an oscillation of frequency some 200-300 times smaller than the"frequency of the valve, itself, there will be only certain, periods,during this relatively low frequency oscillation when the valve is in aposition to oscillate.

If areceived signal is now impressed upon the Lecher system the valvewill break into o-scillation much more rapidly than if there is no suchsignal and the-'start of oscillation has to depend entirely upon randomthermal variations. In consequence, if a signal is being received thevalve will be oscillating on the. average. fora greater proportion ofVits timethan` wouldbe the case if no signal exists. The oscillationofthe valve can be detected by measuring the direct current to. theLecher Wire systems. Itis clear that with the. mode, of oscillationwhich. occurs, the number of. electronsarriving at L willbeconsiderablyaffected by theexistenceof oscillations. Consequentlyeithera sensitive meter or tele. phones in theV circuit of Lwillregisterchangesin the current to Lin a` waysuitableV either fordirect detectionor. for further amplification. The valve in fact whenused as a super-regenerativeV receiver actsA also, as its owndetector.

A number of further variations within the scope .between g andi we havenowtwo different parabolic distributions, one betweenO and l and the.

other between O and y. In order to effectthis, it is necessary that` thetwo` anodeA rods A should be very closetogether, to ensure that thespaces on either. sidel of. these. rods should be well.

shielded l,from one. another. In this case, the mode, of, phaseselection ofthe. electrons. at the Lecher wire lanti-cathodel. isunchanged, and

an electron, instead 4of crossing` from O to Gand.

back to,.O again in half Athe period of the. oscillation of the Lecherwire, nowV does it in ,l1/2 periods It then.. returns, in the same phaseas. itwould have if. the `distance O to G were still identical with thevof the oscillation ofthe Lecherwire.

distance() to L. Thishas, however, the mechan-` ical advantage thatthevspace O toGcan be made. considerably larger forl a given desiredwaver length Without making it necessary for the anodeI potential to be,excessively high. Valves Vof this lop-sided typev oscillateVsatisfactorily down to wave lengthshof 10 cm. atanode potentials notgreater than, 400 to 500 volts.,

A drawback` whichhasgbeenrfound in constructing the valves withyelectrodes arranged symmetrically about thepathode lies lin the fact*the two sides Vof' the valve accurately` alike, Smallv differencesbetween the two sides lead to the pro'- duction of'4 Voscillations inAtwo differentV wave lengths fer the. .Semeoieeiialpeihe anode rede;

These do not, of course, co-exist at any one time, but each can beobtained by tuning the Lecher wire system suitably. This lack ofsymmetry is often inconvenient as the peaks of` current of the Lecherwires, as the external circuit is tuned, often over-lap. This has beenavoided by coating one side of the cathode only (in any case, thecathode is normally coated only in narrow strips opposite to the gapbetween the grid wires G). The necessity for constructing both sides ofthe valve and then using one side only is however a disadvantage and itis best to revert to the single sides structure of Fig. 1 in which thepair of electrodes which are being continued outside the valve as atuned Lecher wire circuit consist oi the grid and electrode L. This alsotakes up less space, which is important when it is remembered that themagnetic eld is essential to the working of the valve. With overalldimensions of the order of 1 cm. or less small permanent magnets asindicated by reference characters M can be used and an adequate eldstill obtained. The 'working length of the electrode system, that is thelength of each rod electrode may be about 2 cm.

It is also proposed to construct the whole tube in metal such as copper,e. g., as shown in Fig. 3. En this gure the parabolic field distributionis set up inherently because of the shape of the conductive envelope.This envelope is shown to comprise two generally cylindrical portions Fand I-I, joined by two preferably integral longitudinally extendingreentrant portions X. The metal envelope is given a positive potential,and the two points X thus correspond to the anode rods of Fig. 1, as faras function is concerned. It is then possible for the electrode L to betuned as the centre of a concentric line, the surrounding envelope beingtuned as the outside of this line. It would be possible of course tohave two cathode and control grid systems, each as shown in Fig. 3,opening orf the concentric line on opposite sides. It would thus bepossible to obtain oscillations of greater amplitude from the system.Since, howeVeI, the Silbe iS Primarily for use as a receiver,

it is probably not convenient or particularly advantageous to do this,as it increases the complication of the construction, and it is easierrather to amplify the signal after detection than to produce a highamplitude initially.

What is claimed is:

1. Electron discharge apparatus including a cathode, a pair of gridmembers each spaced equally from said cathode and spaced from eachother, a pair of accelerating electrode members i..

each spaced equally from said cathode and spaced from each other, thespacing from one of said grid members to one of said acceleratingelectrode members being equal to the spacing of the other of said gridmembers from the other of said accelerating electrode members, ananti-cathode member spaced equally from each of said acceleratingelectrode members, and means producing a magnetic field extending fromsaid cathode to said anti-cathode and generally perpendicular to allsaid members.

2. Electron discharge apparatus including a cathode, a pair of gridmembers each spaced equally from said cathode and spaced from eachother, a pair of acceleratingelectrode members each spaced equally fromsaid cathode and spaced from each other, the spacing from one of saidgrid members to one of said accelerating electrode members being equalto the spacing of the other of said grid members from the other of saidaccelerating electrode members, an anticathode member spaced equallyfrom each of said accelerating electrode members, means producing amagnetic field extending from said cathode to said anti-cathode andgenerally perpendicular to all of said members, a pair of Lecher wires,one of said Lecher Wires being connected to said anticathode, and theother of said Lecher wires being connected to another electrode of saidtube.

3. Electron discharge device comprising a generally cylindrical cathodemember, a plurality ci pairs of grid members each spaced equally fromsaid cathode member, said members of said pairs being spaced from eachother, a corresponding plurality of pairs of accelerating electrodemembers, in each of said corresponding pairs the spacing from one ofsaid accelerating electrode members to one of said grid members beingequal to the spacing of the other of said accelerating electrode membersfrom the other of said grid members, and a. plurality of anti-cathodemembers corresponding to said plurality of pairs ci grid members andaccelerating electrode members, each of said anti-cathode memberscorresponding to a pair of said accelerating electrode members beingspaced equally from each of said last-mentioned accelerating electrodemembers.

4. Electron discharge apparatus according to claim l, in which saidcathode and said members are each generally cylindrically shaped anddisposed in their respective axial directions parallel to one another.

5. Electron discharge apparatus according to claim 1 wherein saidcathode and said grid members are enclosed in an envelope of conductingmaterial, and wherein said pair of accelerating electrode members areformed by two parallel oppositelir disposed reentrant portions formed insaid envelope.

6. An electron discharge device according to claim 2 wherein one of saidLecher wires is connected to said anti-cathode and the other to saidgrid members.

JOHN HEAVER FREMLIN.

